Below are histograms showing all NFL coaches hired since the merger who have coached more than one season, sorted by their regular season and playoff win percentage.
The bar which includes Marvin is in black.

Bad coaching can neutralize even the most talented of athletes. There are two seasons of the year for me: Football Season and waiting for Football Season.Playoff Record: 0-6
Losing 4 consecutive 1st round Playoff Games: not a coincidence